The invention relates to a system for analyzing a sample using an electrochemical cell. The electrochemical cell is provided in a test strip. The test strip is elongated and has the cell at one end (sometimes called the “distal” end) and has a connection region at the other end (sometimes called the “proximal” end). The connector region is shaped to plug into a connector on an apparatus. The apparatus contains electronic circuitry for applying signals to the cell and for monitoring signals received from the cell.
The test strip is made up of layers. In an exemplary embodiment the layers are as described in U.S. patent application No. 60/521,555 filed May 21, 2004, which application is incorporated herein by reference for all purposes. An elongated substrate or carrier provides mechanical rigidity and support. Deposited or painted onto the substrate are conductive paths such as those shown in FIG. 1 at locations 10, 11, 13. FIG. 1 shows a plan view of one of the layers of a strip. These paths may be gold or silver or palladium or conductive carbon. The electrochemical reaction cell is built up in area 12 in FIG. 1. Area 10 defines a “working” electrode of the reaction cell, and the cell also includes a “counter” electrode omitted for clarity in FIG. 1.
Turning ahead to FIG. 2, what is seen is a cross section in a plane that extends along the length of the elongated strip and that is perpendicular to the plane portrayed in FIG. 1. Conductive paths 11, 13, 10 may be seen in FIG. 2 and these are the same paths 11, 13, 10 shown in FIG. 1. Reagent material 14 defines the reaction cell mentioned above, which is in area 12. What may be seen in FIG. 2 (and what was omitted for clarity in FIG. 1) is a conductive path 15, deposited in a plane that is parallel and above the plane of FIG. 1. This path 15, together with other geometry, defines the counter electrode of the reaction cell. Thus the material 14 lies between the working electrode and the counter electrode but (in an exemplary embodiment) does not fill the space between the two electrodes. The dry reagent does not “touch” the counter electrode.
The path 15 (not visible in FIG. 1) extends far enough to overlap with path 11 (visible in FIG. 1). A crossover area 16 is constructed providing an electrically conductive connection between the path 11 and the path 16. It will be appreciated that the structure of the strip typically includes insulating elements and adhesive elements that are omitted for clarity in FIGS. 1 and 2, as well as physical features that provide a place where a fluid of interest (such as blood) may be introduced. When the fluid is introduced, it enters the reaction cell lying between conductive paths 10 and 15 in FIG. 2. The apparatus passes signals into the strip by means of the above-mentioned connector and through paths 10, 11, and 16 to the reaction cell. Returned signals permit the apparatus to analyze particular properties of the fluid. In an exemplary embodiment the fluid is human blood, the reagent material 14 includes a glucose oxidase, and the property being measured is the glucose content of the blood. (More generally instead of glucose oxidase any glucose-responsive enzyme might be employed.)
Exemplary methods and apparatus for such analysis are described in PCT publications WO 2005/022143, WO 03/069304, and WO 2003/060154, each of which is hereby incorporated herein by reference for all purposes.
It would be extremely desirable to devise features of a test strip which would permit testing of the strip to find out whether the conductive paths are being laid down correctly. One problem with many test strip designs is that testing of particular conductive paths risks damaging the paths. With such designs, the very act of testing poses a risk of making the strip less reliable. Destructive testing then leads to lower manufacturing yields. This is an undesirable state of affairs.
It would also be extremely desirable to devise features of a test strip and of the associated analytical apparatus which would permit defining particular test strips as having been made for use in particular geographic regions or for specific customers. Then, in a way which brings to mind the regional coding of DVDs (digital video disks) and DVD players, a strip made for use in a particular region or for a particular customer would work only with an apparatus made for use in that region.
Finally it would be desirable to have a structure of conductors that helps to control the printing of the reagent so that it deposits in the right place.